A team of scientists at Lawrence Livermore National Laboratory (LLNL) has shown that the structure of microscopic pores in high explosive materials can significantly impact performance and safety. These findings — published recently as the cover article in the journal Propellants, Explosives, Pyrotechnics — open the door to the possibility of tuning high explosives by engineering their microstructure.

"The funny thing about explosives is that they have these little defects and pores and holes," said research scientist Keo Springer, lead author on the paper and researcher at LLNL's High Explosives Applications Facility. "It turns out that that's an important part of what makes them work. Explosive performance, in a broad sense, isn't just a chemistry question, it's a microstructure question."

In most high explosives, detonation is initiated through a process where pores get compressed by a shockwave. When a pore collapses, it creates a hotspot capable of initiating a chemical reaction in the microscopic crystalline grains of explosive material. This research focused on an explosive compound called HMX, which is known to be more sensitive and more dangerous to work with than other explosives. The fundamental question at the root of this study was whether it makes a difference if the pores are located in the interior of the grains or on their surface.

"We found out that when pores are at the surface, they speed up the reaction," Springer said. "We also discovered that if a shockwave hits a number of surface pores at once, they bootstrap each other. It's an explosive party, and they party well together."

In addition to pore location, the team examined whether it makes a difference if the porosity is distributed across many small pores or across fewer larger pores. While they showed that many small pores can work together to accelerate one another's burning, they also were able to identify a threshold where pores become so small that the reaction is extinguished.

This examination was conducted in a series of numerical simulations on LLNL supercomputers with the multi-physics code, ALE3D. Next steps for the research team—Springer, along with LLNL scientists Sorin Bastea, Al Nichols, Craig Tarver and Jack Reaugh—include verifying that the numerical simulations capture the real physical and chemical processes. A direct way to do that is to conduct micro-scale experiments to quantify pore collapse mechanisms and reactivity.

"Validation is the tough part," Springer said. "Ideally, we would need a really good magnifying glass and the ability to stop time. We're talking about sub-micron resolution with a shutter speed on the order of nanoseconds. What's neat is that the research community is starting to work on this.

"If we can engineer initiation properties into the microstructure of explosives, it would be a game changer for industry and for the safety of the nuclear stockpile. But we have a long way to go to realize that vision. This type of research is very important, but just one of the first steps."

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

E-mail the story

Uncovering secret structure to safer explosives

Note

Your email address is used only to let the recipient know who sent the email. Neither your address nor the recipient's address will be used for any other purpose.
The information you enter will appear in your e-mail message and is not retained by Phys.org in any form.

Your message

Newsletter sign up

Get weekly and/or daily updates delivered to your inbox.
You can unsubscribe at any time and we'll never share your details to third parties.

Your Privacy

This site uses cookies to assist with navigation, analyse your use of our services, and provide content from third parties.
By using our site, you acknowledge that you have read and understand our Privacy Policy
and Terms of Use.